This invention relates to the monitoring of the movement of sheets in a reproduction machine, and in particular, to a combination mechanical actuator and electro-optic sensor to monitor movement of the sheets.
The monitoring of the movement of copy sheets within a reproduction machine has always been a concern to minimize malfunctions and machine down-time. This problem becomes even more acute with the trend of machines toward higher volumes and faster through-puts. The prior art is replete with mechanical switches and sensors to monitor and control the movement of documents and sheets throughout a reproduction machine. In addition, combination electrooptic sensors and mechanical switches are known.
For example U.S. Pat. No. 4,397,455 discloses a stack height sensor including an arm feeler adapted for rotatable movement such that when the height of the stack changes, an arm indicator has a shoulder that blocks an opto-electrical sensor providing an actuating signal to a motor. U.K. Pat. No. 1,291,662 discloses a stack height sensor including a housing, a vertically translatable plunger supported in the housing, an opto-electrical sensor, and an actuator integral with the plunger adapted for movement into the path of the opto-electrical sensor. Xerox Disclosure Journal, Volume 9, No. 4, July/August 1984 discloses a stack height sensor having a housing and a plunger mounted within the housing under pressure from a compression spring such that an actuator is mounted for movement with the plunger for blocking and unblocking an opto-electrical sensor causing the actuation of a motor to raise an elevator and maintain a predetermined normal force of a feed device against a stack of sheets.
Another major concern in reproduction machines has been reliable paper sensing over the product life, particularly with regard to high volume machines. Sensors are very sensitive to degradation over the life of the machine by such things as mechanical wear, dirt, and other debris within the copier environment. Mechanical contact switches in particular are subject to intolerable wear and tear over the life of the machine, requiring replacement or repair and the time and cost of service calls. A difficulty with the prior art copy sheet sensors and switches such as disclosed above is the susceptibility to wear and tear and degradation over the life of the machine. Another need in copy sheet detectors, particularly in high volume machines is the need for relatively fast responding switches and sensors. Rapid switch and sensor response is necessary for proper monitoring control and internal diagnostics of a high volume machine. A difficulty with prior art devices such as described above is that these prior art switches and sensors are relatively complex and massive and unable to provide a rapid switch response.
It is an object of the present invention therefore to provide a new and improved sheet sensor that resists wear and tear, is reliable over the life of the machine, and provides a relatively rapid response to the detection of sheets within the machine. Further advantages of the present invention will become apparent as the following description procedures, and the features characterizing the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.